Effects of casoxin 4 on morphine inhibition of small animal intestinal contractility and gut transit in the mouse.

Patten GS, Head RJ, Abeywardena MY - Clin Exp Gastroenterol (2011)

Bottom Line:
Chronic opioid analgesia has the debilitating side-effect of constipation in human patients.Using a polymeric dye, Poly R-478, the opioid antagonists casoxin 4 and lactoferroxin A were tested orally for blocking activity of morphine inhibition of gut transit in vivo by single or double gavage techniques.In contrast to naloxone, relatively high oral doses of the μ-opioid receptor antagonists, casoxin 4 and lactoferroxin A, applied before and after morphine injection were unable to antagonize morphine inhibition of gut transit.

Background and aims: Chronic opioid analgesia has the debilitating side-effect of constipation in human patients. The major aims of this study were to: 1) characterize the opioid-specific antagonism of morphine-induced inhibition of electrically driven contraction of the small intestine of mice, rats, and guinea pigs; and 2) test if the oral delivery of small milk-derived opioid antagonist peptides could block morphine-induced inhibition of intestinal transit in mice.

Methods: Mouse, rat, and guinea pig intact ileal sections were electrically stimulated to contract and inhibited with morphine in vitro. Morphine inhibition was then blocked by opioid subtype antagonists in the mouse and guinea pig. Using a polymeric dye, Poly R-478, the opioid antagonists casoxin 4 and lactoferroxin A were tested orally for blocking activity of morphine inhibition of gut transit in vivo by single or double gavage techniques.

Conclusions: Casoxin 4 reverses morphine-induced inhibition of contraction in mice and guinea pigs in vitro but fails to influence morphine inhibition of mouse small intestinal transit by the oral route.

f1-ceg-4-023: Morphine inhibition of electrically driven contractions in guinea pig (▾), rat (○), and mouse (▴) ileum. Mouse was also in the presence (▪) of 0.1 μM ibuprofen. Each point is the mean ± SEM for ileal tissue from 15–19 guinea pigs and 3–4 rats or mice performed in duplicate. Significant differences between species is indicated at 10−8, 10−7, 3 × 10−7, and 10−6 mol/L as determined by 2-way ANOVA and Dunnett post tests as P < 0.01 (letter a) for guinea pig compared with rat or mouse.Abbreviations: ANOVA, analysis of variance; GP, guinea pig; Mo, mouse; SEM, standard error of the mean.

Mentions:
For the mouse, electrical square pulses of 3–5 milliseconds were required to stimulate maximal movement (results not shown) of mouse ileum at 60 V and 0.1 Hz. This resulted in a large relaxation phase that was followed by a smaller contraction phase. The IC50 for morphine inhibition for the electrically driven contractions in the mouse ileum was 180 ± 14 nmol/L (Figure 1). It was found that 0.1 μmol/L ibuprofen reduced the basal tone and routinely abolished the majority of the relaxation phase revealing predominantly the contraction phase of smooth muscle action. However, in this system, ibuprofen did not significantly change the sensitivity to morphine (IC50 230 ± 15 nmol/L), compared with morphine alone, 180 ± 14 nmol/L (Figure 1). In all subsequent experiments, ibuprofen was included 5–10 minutes before the addition of opioid agonist or antagonist. The relative sensitivities to morphine inhibition using the electrical stimulation (IC50 as nmol/L ± SEM) regimens were for the guinea pig (34 ± 3), compared with the mouse (230 ± 15) and rat (310 ± 17), which was significantly lower in the guinea pig compared with both mouse and rat (P < 0.001) and between the mouse and the rat (P < 0.05) as shown in Figure 1 (P < 0.01).

f1-ceg-4-023: Morphine inhibition of electrically driven contractions in guinea pig (▾), rat (○), and mouse (▴) ileum. Mouse was also in the presence (▪) of 0.1 μM ibuprofen. Each point is the mean ± SEM for ileal tissue from 15–19 guinea pigs and 3–4 rats or mice performed in duplicate. Significant differences between species is indicated at 10−8, 10−7, 3 × 10−7, and 10−6 mol/L as determined by 2-way ANOVA and Dunnett post tests as P < 0.01 (letter a) for guinea pig compared with rat or mouse.Abbreviations: ANOVA, analysis of variance; GP, guinea pig; Mo, mouse; SEM, standard error of the mean.

Mentions:
For the mouse, electrical square pulses of 3–5 milliseconds were required to stimulate maximal movement (results not shown) of mouse ileum at 60 V and 0.1 Hz. This resulted in a large relaxation phase that was followed by a smaller contraction phase. The IC50 for morphine inhibition for the electrically driven contractions in the mouse ileum was 180 ± 14 nmol/L (Figure 1). It was found that 0.1 μmol/L ibuprofen reduced the basal tone and routinely abolished the majority of the relaxation phase revealing predominantly the contraction phase of smooth muscle action. However, in this system, ibuprofen did not significantly change the sensitivity to morphine (IC50 230 ± 15 nmol/L), compared with morphine alone, 180 ± 14 nmol/L (Figure 1). In all subsequent experiments, ibuprofen was included 5–10 minutes before the addition of opioid agonist or antagonist. The relative sensitivities to morphine inhibition using the electrical stimulation (IC50 as nmol/L ± SEM) regimens were for the guinea pig (34 ± 3), compared with the mouse (230 ± 15) and rat (310 ± 17), which was significantly lower in the guinea pig compared with both mouse and rat (P < 0.001) and between the mouse and the rat (P < 0.05) as shown in Figure 1 (P < 0.01).

Bottom Line:
Chronic opioid analgesia has the debilitating side-effect of constipation in human patients.Using a polymeric dye, Poly R-478, the opioid antagonists casoxin 4 and lactoferroxin A were tested orally for blocking activity of morphine inhibition of gut transit in vivo by single or double gavage techniques.In contrast to naloxone, relatively high oral doses of the μ-opioid receptor antagonists, casoxin 4 and lactoferroxin A, applied before and after morphine injection were unable to antagonize morphine inhibition of gut transit.

Background and aims: Chronic opioid analgesia has the debilitating side-effect of constipation in human patients. The major aims of this study were to: 1) characterize the opioid-specific antagonism of morphine-induced inhibition of electrically driven contraction of the small intestine of mice, rats, and guinea pigs; and 2) test if the oral delivery of small milk-derived opioid antagonist peptides could block morphine-induced inhibition of intestinal transit in mice.

Methods: Mouse, rat, and guinea pig intact ileal sections were electrically stimulated to contract and inhibited with morphine in vitro. Morphine inhibition was then blocked by opioid subtype antagonists in the mouse and guinea pig. Using a polymeric dye, Poly R-478, the opioid antagonists casoxin 4 and lactoferroxin A were tested orally for blocking activity of morphine inhibition of gut transit in vivo by single or double gavage techniques.

Conclusions: Casoxin 4 reverses morphine-induced inhibition of contraction in mice and guinea pigs in vitro but fails to influence morphine inhibition of mouse small intestinal transit by the oral route.